Optical coherence tomography apparatus, optical fiber lateral scanner and a method for studying biological tissues in vivo

ABSTRACT

In a method for in vivo diagnostics of a biological tissue covered with epithelium an image of the biological tissue is acquired with the aid of a beam in the visible or near IR range directed towards a biological tissue by visualizing the intensity of optical radiation backscattered by the biological tissue. The basal membrane of said biological tissue, which separates the epithelium from an underlying stroma, is identified in the acquired image and diagnostics is performed on basis of the form of the basal membrane. For diagnostics of biological tissue lining the surface of cavities and internal organs of a patient a miniature optical fiber probe is inserted into the patient&#39;s cavity. The probe may be placed at a distal end of an endoscope instrumental channel. Acquired images show that a biological tissue covered with healthy epithelium has a smooth basal membrane, which separates stratified squamous epithelium from underlying connective tissue, while pathological regions of biological tissue are characterized by a change in the shape of the basal membrane, or violation of its integrity, or its absolute destruction. Using low coherent optical radiation for implementing the developed method ensures high spatial in-depth resolution.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application of application Ser. No. 09/623,343,filed Dec. 1, 2000, now U.S. Pat. No. 6,608,684, which is a Section 371of PCT/RU99/00034 filed Feb. 9, 1999.

TECHNICAL FIELD

The present invention relates to physical engineering, in particular, tothe study of internal structure of objects by optical means, and can beapplied for medical diagnostics of individual organs and systems ofhuman body in vivo, as well as for industrial diagnostics, for example,control of technological processes.

BACKGROUND ART

In recent years, there has been much research interest in the opticalcoherence tomography of scattering media, in particular, biologicaltissues. Optical coherence tomography apparatus are fairly well knownand comprise a low coherent light source and an optical interferometer,commonly designed as either a Michelson optical fiber interferometer ora Mach-Zender optical fiber interferometer.

For instance, an optical coherence tomography apparatus known from thepaper by X. Clivaz et,al., “High resolution reflectometry in biologicaltissues”, OPTICS LETTERS, Vol. 17, No. 1, Jan. 1, 1992, includes a lowcoherent light source and a Michelson optical fiber interferometercomprising a beam-splitter optically coupled with optical fiber samplingand reference arms. The sampling arm incorporates an optical fiberpiezoelectric phase modulator and has an optical probe at its end,whereas the reference arm is provided with a reference mirror installedat its end and connected with a mechanical in-depth scanner whichperforms step-by-step alteration of the optical length of this armwithin a fairly wide range (at least several tens of operatingwavelengths of the low coherent light source), which, in turn, providesinformation on microstructure of objects at different depths.Incorporating a piezoelectric phase modulator in the interferometer armallows for lock-in detection of the information-carrying signal, thusproviding a fairly high sensitivity of measurements.

The apparatus for optical coherence tomography reported in the paper byJ. A. Izatt, J. G. Fujimoto et al., Micron-resolution biomedical imagingwith optical coherence tomography, Optics & Photonics News, October1993, Vol. 4, No. 10, p. 14-19 comprises a low coherent light source andan optical fiber interferometer designed as a Michelson interferometer.The interferometer includes a beam-splitter, a sampling arm with ameasuring probe at its end, and a reference arm, whose end is providedwith a reference mirror, movable at constant speed and connected with anin-depth scanner. This device allows for scanning the difference in theoptical lengths of the sampling and reference arms. Theinformation-carrying signal is received in this case using a Dopplerfrequency shift induced in the reference arm by a constant speedmovement of the reference mirror.

Another optical coherence tomography apparatus comprising a low coherentlight source and an optical fiber interferometer having a beam-splitteroptically coupled to a sampling and reference arms is known from RU Pat.No. 2,100,787, 1997. At least one of the arms includes an optical fiberpiezoelectric in-depth scanner, allowing changing of the optical lengthof said interferometer arm by at least several tens of operatingwavelengths of the light source, thus providing information onmicrostructure of media at different depths. Since a piezoelectricin-depth scanner is a low-inertia element, this device can be used tostudy media whose characteristic time for changing of opticalcharacteristics or position relative to the optical probe is very short(the order of a second).

Major disadvantage inherent in all of the above-described apparatus aswell as in other known apparatus of this type is that studies of samplesin the direction approximately perpendicular to the direction ofpropagation of optical radiation are performed either by respectivemoving of the samples under study or by scanning a light beam by meansof bulky lateral scanners incorporated into galvanometric probes. Thisdoes not allow these devices to be applied for medical diagnostics ofhuman cavities and internal organs in vivo, as well as for industrialdiagnostics of hard-to-access cavities. (Further throughout the text, adevice performing scans in the direction approximately perpendicular tothe direction of propagation of optical radiation is referred to as a“lateral scanner” in contrast to a device that allows for scanning thedifference in the optical lengths of interferometer arms referred to asa “in-depth scanner”).

Apparatus for optical coherence tomography known from U.S. Pat. No.5,383,467, 1995 comprises a low coherent light source and an opticalinterferometer designed as a Michelson interferometer. Thisinterferometer includes a beam-splitter, a sampling arm with an opticalfiber sampling probe installed at its end, and a reference arm whose endis provided with a reference mirror connected with an in-depth scanner,which ensures movement of the reference mirror at a constant speed. Theoptical fiber sampling probe is a catheter, which comprises asingle-mode optical fiber placed into a hollow metal tube having a lenssystem and an output window of the probe at its distal end. The opticaltomography apparatus includes also a lateral scanner, which is placedoutside the optical fiber probe and performs angular and/or linearscanning of the optical radiation beam in the output window of theoptical fiber probe. However, although such geometry allows forintroducing the probe into various internal cavities of human body andindustrial objects, the presence of an external relative to the opticalfiber probe lateral scanner and scanning the difference in the opticallengths of the sampling and reference arms by means of mechanicalmovement of the reference mirror significantly limit the possibility ofusing this device for performing diagnostics of surfaces of humancavities and internal organs in vivo, as well as for industrialdiagnostics of hard-to-access cavities.

Apparatus for optical coherence tomography known from U.S. Pat. No.5,582,171, 1996 comprises a low coherent light source and an opticalfiber interferometer designed as a Mach-Zender interferometer havingoptical fiber sampling and reference arms and two beam-splitters. Thereference arm includes a unit for changing the optical length of thisarm. This unit is designed as a reference mirror with a spiralreflective surface arranged with a capability of rotating and isconnected with a driving mechanism that sets the reference mirror inmotion. The sampling arm is provided with an optical fiber probe havingan elongated metal cylindrical body with a throughhole extendingtherethrough, and an optical fiber extending through the throughhole. Alateral scanner is placed at the distal end of the probe, which lateralscanner comprises a lens system, a rotatable mirror, and a micromotorfor rotating the mirror, whereas an output window of the probe islocated in the side wall of the cylindrical body. This device allowsimaging of walls of thin vessels, but is unsuitable as a diagnosticmeans to image surfaces of cavities and internal organs inside a humanbody, as well as for industrial diagnostics of hard-to-accesslarge-space cavities.

Another optical coherence tomography apparatus is known from U.S. Pat.No. 5,321,501, 1994 and comprises a low coherent light source opticallycoupled with an optical fiber Michelson interferometer, which includes abeam-splitter and optical fiber sampling and reference arms. Thereference arm has a reference mirror mounted at its end and connectedwith an in-depth scanner. The latter performs movement of the referencemirror at a constant speed, thereby changing the optical length of thisarm by at least several tens of operating wavelengths of the lightsource. The interferometer also comprises a photodetector whose outputis connected with a data processing and displaying unit, and a source ofcontrol voltage connected with the in-depth scanner. The sampling armincorporates an optical fiber probe having an elongated body with athroughhole extending therethrough, wherein a sheath with an opticalfiber embedded in it extends through the throughhole. The sheath isattached to the stationary body through a pivot joint. The probe bodycontains also a lateral scanner comprising a bearing support, anactuator, and a lens system. The actuator includes a moving part and astationary part, whereas the bearing support, the stationary part of theactuator and the lens system are mechanically connected with the probebody. The fiber-carrying sheath rests on the moving part of theactuator. The actuator may be a piezoelectric element, stepper motor,electromagnetic system or electrostatic system. The distal part of theprobe body includes a lens system, the end face of the distal part ofthe optical fiber being optically coupled with the lens system, whereasthe actuator is connected with a source of control current. The outputof the data processing and displaying unit of the optical fiberinterferometer is the output of the apparatus for optical coherencetomography. A disadvantage of this apparatus is that it is not fit fordiagnostics of surfaces of hard-to-access internal human organs in vivo,such as, for example, stomach and larynx, and for industrial diagnosticsof surfaces of hard-to-reach cavities of technical objects. That is dueto the fact that the optical fiber probe in this apparatus must haverelatively large dimensions since maximum movement of the optical fiberrelative to the size of the actuator cannot be more than 20%, because ofthe moving part of the actuator being positioned at one side of thefiber-carrying sheath. Besides, the mechanical movement of the referencemirror at a constant speed used for scanning the difference in opticallengths of the reference and sampling arms restricts the range ofobjects, which can be studied in vivo by this apparatus, or by any otherapparatus of this kind, to those objects whose optical characteristicsand position relative to the optical probe do not change practically inthe process of measurements.

In prior art there are known optical fiber lateral scanners whichcomprise a stationary part, including a bearing support, anelectromagnet, and a lens system, and a moving part including apermanent magnet attached to an optical fiber (see, e.g., U.S. Pat. No.3,470,320, 1969, U.S. Pat. No. 5,317,148, 1994). In these devices, theoptical fiber is anchored at one end to a bearing support and serves asa flexible cantilever, whereas the free end of the optical fiber isarranged such, that it can move in the direction perpendicular to itsown axis. The permanent magnet is placed in a gap between the poles ofthe electromagnet. A disadvantage of devices of this type is that theamplitude of optical fiber deflection is limited by the allowable massof the magnet fixedly attached to the optical fiber (from the point ofview of sagging), and by difficulties in inducing alternate magneticfield of sufficient strength when the device is to have smalldimensions.

Another optical fiber lateral scanner according to U.S. Pat. No.4,236,784, 1979 also comprises a stationary part, which includes abearing support, an electromagnet, and a lens system, and a moving part,including a permanent magnet. In this device, the permanent magnet ismade as a thin film of magnetic material coated onto the optical fiber,whereas the electromagnet is arranged as an array of thin-filmconductors on a substrate layer that is placed orthogonal relative tothe end face of the optical fiber. In this device the small mass of themagnet limits the strength of the induced field, which, in turn, limitsthe amplitude of optical fiber deflection. An increase in the amplitudeof deflection due to an increase in the field strength is impossiblesince this would require currents much exceeding damaging currents forthin-film conductors. Besides, the array of thin-film conductors, beingpositioned across the direction of propagation of an optical radiationbeam, disturbs the continuity of scanning, thus resulting in loss ofinformation.

Another optical fiber lateral scanner comprising a stationary part and amoving part is known from U.S. Pat. No. 3,941,927, 1976. The stationarypart comprises a bearing support, a permanent magnet, and a lens system,whereas the moving part includes a current conductor arranged as aconductive coating on the optical fiber. The optical fiber is placed ina gap between the pole pieces of the permanent magnet and fixedlyattached to the bearing support so that its free end can move in thedirection approximately perpendicular to its own axis, and serves as aflexible cantilever. The end face of the distal part of the opticalfiber is optically coupled with the lens system, whereas the currentconductor is connected with a source of control current. In this devicethe field strength induced by the current conductor, when controlcurrent is applied, is limited by a small mass of the conductivecoating, thus limiting the deflection amplitude of the optical fiber.Due to allocation of the optical fiber between two pole pieces of thepermanent magnet, the overall dimensions of the device are relativelylarge. Thus, a disadvantage of this lateral scanner, as well as of otherknown lateral scanners, is that it is impossible to provide necessaryperformance data, in particular, miniature size, simultaneously withrequired deflection amplitude of the optical fiber to incorporate such adevice in an optical fiber probe of an optical fiber interferometer,which is part of a device for optical coherence tomography suited fordiagnostics of surfaces of hard-to-access human internal organs in vivo,as well as for industrial diagnostics of hard-to-reach cavities.

A particular attention has been given lately to studies of biologicaltissues in vivo. For instance, a method for studying biological tissuein vivo is known from U.S. Pat. No. 5,321,501, 1994 and U.S. Pat. No.5,459,570, 1995, in which a low coherent optical radiation beam at agiven wavelength is directed towards a biological tissue under study,specifically ocular biological tissue, and to a reference mirror alongthe first and the second optical paths, respectively. The relativeoptical lengths of these optical beam paths are changed according to apredetermined rule; radiation backscattered from ocular biologicaltissue is combined with radiation reflected from a reference mirror. Thesignal of interference modulation of the intensity of the opticalradiation, which is a result of this combining, is used to acquire animage of the ocular biological tissue. In a particular embodiment, a lowcoherent optical radiation beam directed to biological tissue understudy is scanned across the surface of said biological tissue.

A method for studying biological tissue in vivo is known from U.S. Pat.No. 5,570,182, 1996. According to this method, an optical radiation beamin the visible or near IR range is directed to dental biological tissue.An image is acquired by visualizing the intensity of scatteredradiation. The obtained image is then used for performing diagnostics ofthe biological tissue. In a particular embodiment, a low coherentoptical radiation beam is used, which is directed to dental tissue, saidbeam being scanned across the surface of interest, and to a referencemirror along the first and second optical paths, respectively. Relativeoptical lengths of these optical paths are changed in compliance with apredetermined rule; radiation backscattered from the dental tissue iscombined with radiation reflected by the reference mirror. A signal ofinterference modulation of intensity of the optical radiation, which isa result of said combining, is used to visualize the intensity of theoptical radiation backscattered from said biological tissue. However,this method, as well as other known methods, is not intended forperforming diagnostics of biological tissue covered with epithelium.

DISCLOSURE OF INVENTION

The object of the present invention is to provide an apparatus foroptical coherence tomography and an optical fiber lateral scanner whichis part of said optical coherence tomography apparatus, with improvedperformance data, both these devices being suited for diagnostics ofsoft and hard biotissue in vivo, in particular, for performingdiagnostics of human cavity surfaces and human internal organs, fordiagnostics of dental, bony, and cartilage biotissues, as well as forindustrial diagnostics of hard-to-access cavities of technical objects.Another object of the invention is to provide a method for diagnosticsof biotissue in vivo allowing for diagnostics of biotissue covered withepithelium, in particular, of biotissue lining the surface of humaninternal organs and cavities.

The developed apparatus for optical coherence topography, similarly todescribed above apparatus known from U.S. Pat. No. 5,321,501 comprises alow coherent light source and an optical fiber interferometer. Theinterferometer includes a beam-splitter, a sampling and referenceoptical fiber arms, a photodetector, a data processing and displayingunit, and a source of control voltage. The beam-splitter, sampling andreference optical fiber arms, and the photodetector are mutuallyoptically coupled, the output of said photodetector being connected withsaid data processing and displaying unit. At least one of the armscomprises an in-depth scanner having a capability of changing theoptical length of said interferometer arm by at least several tens ofoperating wavelengths of the light source. The sampling arm includes aflexible part, which is made capable of being introduced into aninstrumental channel of an endoscope or borescope and is provided withan optical fiber probe having an elongated body with a throughholeextending therethrough, an optical fiber extending through thethroughhole, and an optical fiber lateral scanner. The distal part ofthe optical fiber is arranged to allow for deflection in the directionapproximately perpendicular to its own axis. The optical fiber lateralscanner comprises a stationary part mechanically connect with theoptical fiber probe body and a moving part. The stationary part includesa bearing support, a magnetic system and a lens system. The end surfaceof the distal part of the optical fiber is optically coupled with thelens system, while the lateral scanner is connected with a source ofcontrol current. The reference arm has a reference mirror installed atits end, where the in-depth scanner is connected with a source ofcontrol voltage. The output of the data processing and displaying unitis the output of the optical coherence tomography apparatus.

Unlike the known apparatus for optical coherence tomography, accordingto the invention the optical fiber probe is designed miniature, whereasthe moving part of the lateral scanner comprises a current conductor andsaid optical fiber, which is rigidly fastened to the current conductor.The optical fiber serves as a flexible cantilever, its proximal partbeing fixedly attached to the bearing support. The current conductor isarranged as at least one loop, which envelopes the magnetic system inthe area of one of its poles. A part of the optical fiber is placed inthe area of said pole of the magnetic system, while the plane of theloop of the current conductor is approximately perpendicular to thedirection between the poles of the magnetic stem. The current conductoris connected with the source of control current.

In one embodiment, the magnetic system includes a first permanentmagnet.

In a particular embodiment, the first permanent magnet is provided witha groove extensive in the direction approximately parallel to the axisof the optical fiber, said optical fiber being placed into said groove.

In another particular embodiment, the magnetic system additionallycomprises a second permanent magnet with one pole facing the analogouspole of the first permanent magnet, which is enveloped by the currentconductor. Besides, said one pole of the second permanent magnet islocated near to the optical fiber.

In another embodiment the second permanent magnet has a groove made inthe direction approximately parallel to the axis of the optical fiber.

In a different embodiment the first and second permanent magnets arealigned at their analogous poles, while the optical fiber is placed intoa throughhole extending therethrough in a direction approximatelyparallel to the axis of the optical fiber, the throughhole being formedby facing grooves made in said analogous poles of the permanent magnets.

In another embodiment the current conductor envelopes the secondpermanent magnet.

It is advisable to shape the magnetic system as a parallelepiped.

In one particular embodiment an output window of the optical fiber probeis arranged near the image lane of the end face of the distal part ofthe optical fiber. It is advisable to place the outer surface of theoutput window at the front boundary of the zone of sharp imaging.

In another embodiment the output window of the optical fiber probe is aplane-parallel plate. In the longitudinal throughhole of the body of theoptical fiber probe between the lens system and the plane-parallel platethere may be additionally installed a first prism, at least oneoperating surface of said first prism being antireflection coated.

In a different embodiment the output window of the optical fiber probeis made as a second prism.

It is advisable to make the output window of the optical fiber probehermetically closed.

In one embodiment the source of control current is placed outside thebody of the optical fiber probe.

In another particular embodiment the source of control current is placedinside the body of the optical fiber probe and is designed as aphotoelectric converter.

In other embodiments of the optical fiber interferometer it is advisableto make the body of the optical fiber probe as a hollow cylinder, and touse anizotropic single-mode optical fiber.

It is advisable to make changeable a part of the sampling arm of theinterferometer, including the part being introduced into an instrumentalchannel of an endoscope or borescope, the changeable part of saidsampling arm being connected by a detachable connection with the mainpart of the sampling arm.

It is advisable to make disposable the changeable part of the samplingarm of interferometer.

In a particular embodiment the distal end of the optical fiber probe ismade with changeable tips.

The developed optical fiber lateral scanner, similarly to describedabove optical fiber lateral scanner known from U.S. Pat. No. 3,941,927,comprises a stationary part and a moving part. The stationary partincludes a bearing support, a magnetic system, and a lens system, saidmagnetic system comprising a first permanent magnet. The moving partincludes a movable current conductor and an optical fiber rigidlyfastened to the current conductor. The optical fiber serves as aflexible cantilever and is fixedly attached to the bearing support witha capability for a distal part of said optical fiber of being deflectedin a direction approximately perpendicular to its own axis. The end faceof the distal part of the optical fiber is optically coupled with thelens system, whereas the current conductor is connected with a source ofcontrol current.

Unlike the known optical fiber lateral scanner, according to theinvention the current conductor is made as at least one loop, whichenvelopes the first permanent magnet in the area of one of its poles. Apart of the optical fiber is located in the area of said pole of thefirst permanent magnet, whereas the plane of the loop of the currentconductor is approximately perpendicular to the direction between thepoles of the first permanent magnet.

In a particular embodiment the first permanent magnet is provided with agroove extensive in a direction approximately parallel to the axis ofthe optical fiber, said optical fiber being placed into said groove.

In another embodiment the magnetic system additionally comprises asecond permanent magnet, with one pole facing the analogous pole of thefirst permanent magnet, which is enveloped by said current conductor.Besides, said one pole of the second permanent magnet is located near tothe optical fiber.

In a different embodiment the permanent magnets are aligned at theiranalogous poles, whereas the optical fiber is placed into a throughholeextending therethrough in a direction approximately parallel to the axisof the optical fiber, the throughhole being formed by the facing groovesmade in said analogous poles of the permanent magnets.

It is advisable to have the current conductor additionally envelope thesecond permanent magnet.

It is preferable to shape said magnetic system as a parallelepiped.

In one embodiment the optical fiber, bearing support, magnetic systemand lens system are elements of an optical fiber probe incorporated intoan optical fiber interferometer and are encased into an elongated bodywith a throughhole extending therethrough, the optical fiber extendingthrough the throughhole. The bearing support, magnetic system and lenssystem are mechanically connected with the body of the optical fiberprobe.

In one embodiment the body of the optical fiber probe is made as ahollow cylinder.

In another particular embodiment an output window of the optical fiberprobe is located near the image plane of the end face of the distal partof the optical fiber. It is advisable to place the outer surface of theoutput window of the optical fiber probe at the front boundary of a zoneof sharp imaging.

In a different embodiment the output window of the optical fiber probeis made as a plane-parallel plate. The operating surfaces of theplane-parallel plate are cut at an angle of several degrees relative tothe direction of propagation of optical radiation incident on the outputwindow. The inner surface of the plane-parallel plate may be madeantireflection coated.

In a particular embodiment a first prism is additionally installed inthe longitudinal throughhole in the body of the optical fiber probebetween the lens system and the plane-parallel plate. At least oneoperating surface of this prism is antireflection coated.

In another particular embodiment the output window of the optical fiberprobe is made as a second prism. The inner surface of the second prismmay be antireflection coated.

It is advisable to make the output window of the optical fiber probehermetically closed.

In a particular embodiment the bearing support is located in theproximal part of the longitudinal throughhole in the optical fiber probebody. The proximal part of the optical fiber is fastened to the bearingsupport. The current conductor may be connected with a source of controlcurrent via electrodes attached to the bearing support.

In the developed lateral scanner it is advisable to use anizotropicsingle-mode fiber.

In some embodiments the optical fiber probe is made disposable.

In some other embodiments the distal end of the optical fiber probe ismade with changeable tips.

The developed method for studying biological tissue in vivo, similarlyto the described above method known from U.S. Pat. No. 5,570,182,comprises the steps of directing a beam of optical radiation in thevisible or near IR range towards a biological tissue under study andacquiring subsequently an image of said biological tissue by visualizingthe intensity of optical radiation backscattered by biological tissueunder study to use said image for diagnostic purpose.

Unlike the known method for studying biological tissue in vivo,according to the invention the biological tissue under study is abiological tissue covered with an epithelium, whereas in the acquiredimage the basal membrane of said biological tissue is identified, whichseparates the epithelium from an underlying stroma, and performingdiagnostics of said biological tissue under study on basis of the stateof the basal membrane.

In a particular embodiment said biological tissue is the biologicaltissue lining the surface of human cavities and internal organs. Whendirecting the beam of optical radiation towards said biological tissue,a miniature optical fiber probe is inserted into the cavity under study,through which said beam of optical radiation is transmitted from theproximal end of the probe to its distal end, whereas said beam ofoptical radiation is scanned over said surface under study in compliancewith a predetermined rule.

In a particular embodiment in order to insert the miniature opticalfiber probe into said human cavity under study, the probe is placed intothe instrumental channel of an endoscope.

In another embodiment a low coherent optical radiation beam is used assaid optical radiation beam, which is split into two beams. The beamdirected towards said biological tissue is the first beam, whereas thesecond beam is directed towards a reference mirror, the difference inthe optical paths for the first and second beams being varied incompliance with a predetermined rule by at least several tens ofwavelengths of said radiation. Radiation backscattered from saidbiological tissue is combined with radiation reflected from thereference mirror. The signal of interference modulation of intensity ofthe optical radiation, which is a result of this combining, is used tovisualize the intensity of optical radiation backscattered from saidbiological tissue.

In the present invention the moving part of the lateral scanner in theoptical fiber probe is designed comprising a current conductor, whichenvelopes the magnetic system in the area of one of its poles, and anoptical fiber, which is rigidly fastened to the current conductor,whereas the optical fiber serves as a flexible cantilever. That allowsmaking smaller the overall dimensions of the optical fiber probe incomparison with known arrangements. The magnetic system includes twopermanent magnets aligned at their analogous poles, whereas the opticalfiber is placed in a throughhole extending therethrough in a directionapproximately parallel to the axis of the optical fiber, the throughholebeing formed by the facing grooves made in said analogous poles of thepermanent magnets. This configuration ensures optimization of the probedesign from the point of view of acquisition of maximum amplitude ofdeviation of the beam of optical radiation (±1 mm), whereas havinglimited dimensions of the optical fiber probe, namely, its length is nomore than 27 mm, and diameter is no more than 2.7 mm. This allows formaking the optical fiber probe as a miniature optical fiber probe, whichcan be installed in the distal end of the instrumental channel of anendoscope or borescope, the optical fiber probe being incorporated intothe sampling arm of the optical fiber interferometer which is part ofapparatus for optical coherence tomography. One part of the sampling armof the optical fiber interferometer is made flexible, thus allowing forinserting it into said channels. Miniature dimensions of the opticalfiber probe as well as the flexible arrangement of the sample arm allowto bring up the optical radiation to the hard to access parts ofbiological tissue of internal human organs and cavities, including softbiological tissue (for example, human mucosa in gastrointestinal tracts)and hard biological tissue (for example, dental, cartilage and bonytissue). That makes it possible to use the developed apparatus foroptical coherence tomography together with devices for visual studyingof biological tissue surfaces, for example, with devices for endoscopicstudying of human gastrointestinal and urinary tracts, laparoscopictesting of abdominal cavity, observing the process of treatment ofdental tissue. Using an output window allows to arrange the opticalfiber probe hermetically closed, which, in turn, allows for positioningthe optical fiber probe directly on the surface of object under study,in particular, biological tissue. Having the outer surface of the outputwindow at the front boundary of a zone of sharp imaging ensures highspatial resolution (15-20 μm) during scanning of a focused optical beamalong the surface of object under study. Arranging the source of controlcurrent as a photoelectric transducer and locating it inside the body ofthe optical fiber probe allows to avoid introducing electrical cordsinto the instrumental channel. Having antireflection coated innersurface of the output window designed either as a plane-parallel plateor as a prism allows for a decrease in losses of optical radiation,whereas having beveled operating sides of the plane-parallel plateeliminates reflection from the object-output window boundary. Usinganizotropic optical fiber excludes the necessity of polarization controlin process of making measurements, whereas using a single-mode opticalfiber allows for more simple and lower-cost realization of the device.

In vivo diagnostics of biological tissue covered with epithelium onbasis of the state of basal membrane, according to the developed method,allows for early non-invasive diagnostics of biological tissue. The useof the optical fiber probe of the invention, of which the lateralscanner of the invention is a part, allows for diagnostics of the stateof biological tissue lining the surface of hard-to-access cavities andinternal organs of a patient, for example, by placing the optical fiberprobe into an instrumental channel of an endoscope. Using low coherentoptical radiation for implementing the developed method ensures highspatial in-depth resolution.

BRIEF DESCRIPTION OF DRAWINGS

The features and advantages of the invention will be apparent from thefollowing detail description of preferred embodiments with reference tothe accompanying drawings, in which:

FIG. 1 is a schematic diagram of one particular embodiment of thedeveloped apparatus for optical coherence tomography suitable forimplementing the developed method for studying biological tissue invivo.

FIG. 2 is a cross-sectional view of one particular embodiment of thedeveloped miniature optical fiber probe.

FIGS. 3, 4 are general views of particular embodiments of the developedoptical fiber lateral scanner.

FIGS. 5A, 5B, and 5C are cross-sectional views of particular embodimentsof a distal part of the developed optical fiber probe.

FIGS. 6A and 6B are schematic diagrams of particular embodiments of theinterferometer arm comprising an in-depth scanner.

FIGS. 7A, 7B, 7C, 7D, and 7E are images of a uterine cervix obtained byusing the developed method.

FIG. 8A shows a tomographic image of a front abdominal wall, FIG. 8Bshows the structure of a tooth with a compomer filling.

MODES FOR CARRYING OUT THE INVENTION

The operation of the developed apparatus for optical coherencetomography and the developed optical fiber probe will be best understoodfrom the following description of carrying out the method fordiagnostics of biological tissue in vivo.

The method for diagnostics of biological tissue in vivo is carried outthe following way.

An optical beam in the visible or IR range is directed, for instance,with the aid of a laser, toward a biological tissue under study, thelater being a biological tissue covered with epithelium. An image of thebiological tissue covered with epithelium is obtained by visualizing theintensity of back-scattered optical radiation beam with, for example, aconfocal microscope. In the acquired image, the basal membrane isidentified, which separates the epithelium from underlying stroma.Diagnostics is made on basis of the state of said basal membrane.

In a specific embodiment, said biological tissue covered with epitheliumis a biological tissue lining the surface of cavities and internalorgans of a patient. In this case, when directing an optical beam tosaid biological tissue, a miniature optical fiber probe 8 is insertedinto patient's cavity under study (one embodiment of the probe is shownin FIG. 2). It is advisable to place probe 8 at the distal end of theinstrumental channel of an endoscope. Said optical radiation beam istransmitted through probe 8 from its proximal end to its distal end.Scanning of said optical radiation beam is performed along the surfaceunder study in accordance with a predetermined rule.

In a preferred embodiment of the method an optical low coherentradiation beam is used as the optical radiation beam. This embodiment ofthe developed method may be realized with the aid of the device, aschematic diagram of which is shown in FIG. 1, and with the aid of anoptical fiber probe shown in FIG. 2, as follows.

Optical fiber probe 8 is installed at the distal end of the instrumentalchannel of an endoscope (not shown in the drawing), the outer surface ofan output window 31 of optical fiber probe 8 is brought into contactwith the biological tissue lining the surface of cavities and internalorgans of a patient under study. It must be noted that for someembodiments for better serviceability a part of sampling optical fiberarm 4 of an interferometer 2 may be made changeable, specifically,disposable, and in this case it is connected with the main part ofsampling arm 4 by a detachable connection (not shown in the drawing). Anoptical low coherent radiation beam is formed using a source 1, whichcan be arranged, for example, as a superluminiscent diode. This opticalradiation beam passes to optical fiber interferometer 2, which is aMichelson interferometer, and is then split into two beams by means of abeam-splitter 3 of optical fiber interferometer 2. The first beam isdirected toward biological tissue under study using optical fibersampling arm 4 and optical fiber probe 8. Said beam is scanned over thesurface under study in compliance with a predetermined rule usingoptical fiber probe 8 as follows.

An optical fiber 13, which may be a PANDA-type optical fiber, extendsthrough a throughhole 12 of an elongated body 11 of optical probe 8 andprovides for propagation of the first low coheren□e optical radiationbeam from a proximal part 20 of optical fiber 13 to its distal part 14.Body 11 of optical fiber probe 8 may be made of stainless steel. In aparticular embodiment the length of body 11 is no more than 27 mm,whereas its diameter is no more than 2.7 mm.

Body 11 comprises also a lateral scanner 15 (see also FIG. 3 and FIG. 4)which is connected with a source of control current (not shown in thedrawing). Said source of control current may be located inside body 11of optical fiber probe 8 and may be arranged as a photoelectricconverter (not shown in the drawing). Lateral scanner 15 has astationary part, which is mechanically connected with body 11 andincludes a bearing support 16, magnetic system 17, and lens system 18,and a moving part, which includes a current conductor 19 and opticalfiber 13, which serves as a flexible cantilever and is rigidly fastenedto current conductor 19 which may be made of insulated copper wire.Referring to FIG. 1, bearing support 16 is placed in the proximal partof a throughhole 12 of body 11, proximal part 20 of optical fiber 13being fixedly attached to bearing support 16. By the way, bearingsupport 16 may be located between magnetic system 17 and lens system 18,magnetic system 17 being placed in the proximal part of throughhole 12of body 11, whereas a middle part of optical fiber 13 is connected withbearing support 16 (this embodiment is not shown in a drawing). A distalpart 14 of optical fiber 13 is placed so that it can be deflected in thedirection A—A, approximately perpendicular to its own axis. The end face21 of distal part 14 of optical fiber 13 is optically coupled with lenssystem 18.

Magnetic system 17 of lateral scanner IS shown in FIG. 3 comprises afirst permanent magnet 22, which has a groove 23 extensive in adirection approximately parallel to the axis of optical fiber 13,whereas optical fiber 13 is placed in said groove 23. Current conductor19 is arranged as at least one loop 24 of wire which envelopes magneticsystem 17, i.e., first permanent magnet 22, in the area of one of itspoles 25. A part 26 of optical fiber 13 is placed in the area of pole25. The plane of loop 24 of current conductor 19 is approximatelyperpendicular to the direction between poles of permanent magnet 22.Current conductor 19 via electrodes 27, which are fixed on bearingsupport 16, is connected with a source of control current (not shown inthe drawing) which is placed outside body 11.

In a particular embodiment of lateral scanner 15 indicated in FIG. 4magnetic system 17 additionally includes a second permanent magnet 28.First and second magnets, 22 and 28, respectively, are aligned at theiranalogous poles 25 and 29, whereas magnets 22 and 28 are used to form astationary magnetic field and may be made from NiFeB material. Opticalfiber 13 is placed into a throughhole 30 extending therethroughapproximately parallel to the axis of optical fiber 13. The throughhole30 is formed by facing grooves made in aligned poles 25, 29 of permanentmagnets 22 and 28. Diameter of throughhole 30 is determined bypredetermined amplitude of deflection of optical fiber 13 with maximummagnetic field intensity in the area of current conductor 19. Currentconductor 19 envelopes permanent magnets 22, 28 in the area of theiraligned poles 25, 29.

An output window 31 of optical fiber probe 8 is placed near to the imageplane of end face 21 of distal part 14 of optical fiber 13. In oneembodiment shown in FIGS. 4 and 5A, an output window 31 is arranged as aplane-parallel plate 32. Plane-parallel plate 32 is opticallytransparent in the range of operating frequencies, being made ofmaterial allowed for use in medical purposes. Bevel angle of theoperating sides of plane-parallel plate 32 relative to the direction ofpropagation of optical radiation beam incident on output window 31 isdetermined by a given level of reflections of the optical radiation beamfrom the front side of plane-parallel plate 32 to the viewing angle ofthe optical system and must not be more than an angle of divergence ofthe optical radiation beam. In embodiment shown in FIG. 5A, operatingsides of plane-parallel plate 32 are cut at an angle of several degreesrelative to the direction of propagation of the optical radiationincident on output window 31. A first prism (not shown in the drawing)may be additionally installed between lens system 18 and plane-parallelplate 32. Referring to FIGS. 5B and 5C output window 31 is made as asecond prism 33, which may have various configurations. First prism andsecond prism 33 are used to provide lateral view on surface under studywith the aid of optical fiber probe 8. Specific configurations of saidprisms are defined by a predetermined angle of lateral view. The valuesof refractive index of plate 32 and prism 33 are chosen such as toprovide a minimum level of reflections from the boundary “output window31—surface under study” and must be maximally close to the refractiveindex value of the object under study. The inner surfaces ofplane-parallel plate 32 and prism 33 are 20 made antireflection coatedin order to decrease losses. The distal part of optical fiber probe 8,which includes output window 31, may be made with changeable tips.

Magnetic system 17 of lateral scanner 15 ensures establishing of astationary magnetic field. The field lines of the magnetic field inducedby magnetic system 17 are situated in the plane of loop 24 of currentconductor 19 and cross the loop 24 in the direction approximatelyorthogonal to the direction of the current in the loop 24 of currentconductor 19. So, when control current is applied in current conductor19, there occurs a force that affects current conductor 19 in thedirection approximately orthogonal to the plane of loop 24 of currentconductor 19. This force being proportional to the current strength incurrent conductor 19 and to the intensity of stationary magnetic fieldinduced by magnetic system 17, causes respective movement of currentconductor 19. Since the proximal part 20 of optical fiber 13 is fastenedin bearing support 16 as a free cantilever, and current conductor 19 isrigidly fixed to optical fiber 13, then when control current is appliedin current conductor 19, there occurs a deflection of distal part 14 ofoptical fiber 13 in the direction approximately perpendicular to its ownaxis. In a particular embodiment an amplitude of this deflection ofdistal part 14 of optical fiber 13 is ±0.5 mm. Lens system 18 ensuresfocusing of the optical radiation beam that has passed through opticalfiber 13 onto the surface of biological tissue under study.

The second optical radiation beam by means of reference arm 5 isdirected to a reference mirror 9. Reference arm 5 contains an in-depthscanner 10 connected with a source of control voltage (not shown in thedrawing). With the aid of in-depth scanner 10 the difference in theoptical lengths of arms 4,5 of interferometer 2 is changed at a constantvelocity V by at least several tens of operating wavelengths of lightsource 1.

Referring to FIG. 1, reference mirror 9 is stationary, whereas in-depthscanner 10 is made as an optical fiber piezoelectric transducer knownfrom RU Pat. No. 2,100,787 (U.S. Pat. No. 5,867,268). In this embodimentin-depth scanner 10 comprises at least one body which has piezoelectricproperties, exhibits a high perpendicular inverse piezoeffect, and hasan electric field vector when an electric field is applied toelectrodes, which are mechanically connected with said body, whereas anoptical fiber is mechanically connected with said electrodes. Adimension of said piezoelectric body in a direction substantiallyperpendicular with said electric field vector is essentially larger thana dimension of said body in a direction substantially aligned with saidelectric field vector. The length of the optical fiber exceedssubstantially the diameter of said piezoelectric body.

In-depth scanner 10 may be made analogous with in-depth scannersdescribed in U.S. Pat. No 5,321,501. In this case, reference mirror 9 ismade movable at a constant speed, and in-depth scanner 10 beingconnected with reference mirror 9, may be made as mechanisms ofdifferent types providing for necessary moving of reference mirror 9(FIG. 6A).

In-depth scanner 10 may be designed according to the paper by K. F.Kwong, D. Yankelevich et al, “400-Hz mechanical scanning optical delayline”; Optics Letters; Vol. 18, No. 7, Apr. 1, 1993, as a dispersegrating delay line (FIG. 6B) comprising a first lens 34, diffractiongrating 35 and second lens 36, all these elements being arranged inseries along the optical axis. Second lens 36 is optically coupled withreference mirror 9 placed so that it can swing relative to the directionof propagation of incident optical radiation.

Using beam-splitter 3 the radiation backscattered from said biologicaltissue is combined with the radiation reflected from reference mirror 9.Changing the difference in the optical lengths of arms 4,5 with in-depthscanner 10 leads to interference modulation of intensity of combinedoptical radiation at the output of beam-splitter 3 at a Dopplerfrequency f=2V/λ, where λ is the operating wavelength of source 1.Besides, the rule of interference modulation corresponds to the changein the intensity of optical radiation backscattered from biologicaltissue under study at different depths. Then an image of biologicaltissue under study is acquired by visualizing intensity of opticalradiation backscattered from biological tissue under study by using thesignal of interference modulation of intensity of the optical radiation,which is the result of said combining, as follows.

A photodetector 6 provides for conversion of the combined opticalradiation from the output of beam-splitter 3 into an electrical signalwhich arrives at a processing and displaying unit 7. Unit 7 is used toform images of an object under study by visualizing the intensity ofback-scattered coherent radiation and may be made, for example,similarly to the data processing and displaying unit discussed in thepaper by V. M. Gelikonov et al., “Coherent optical tomography ofmicroinhomogeneities in biological tissues” JETP Lett., v. 61, No 2, pp.149-153. This data processing and displaying unit comprises a band-passfilter, a log amplifier, an amplitude detector, an analog-to-digitalconverter, and a computer, all these elements being connected in series.Band-pass filter of unit 7 sorts the signal at a Doppler frequency,thereby improving the signal-to-noise ratio. Once the signal isamplified, it arrives at a detector that sorts a signal proportional tothe waveform envelope of this signal. The signal sorted by the amplitudedetector of unit 7 is proportional to the signal of interferencemodulation of intensity of the combined optical radiation.Analog-to-digital converter of unit 7 converts the signal from theoutput of the amplitude detector into a digital format. Computer of unit7 provides for acquisition of images by displaying on a video monitorthe intensity of the digital signal (said displaying may be performed asdescribed, for instance, in the paper by H. E. Burdick “Digital imaging:Theory and Applications”, 304 pp., Mc Graw Hill, 1997). Since thedigital signal corresponds to the change in intensity of opticalradiation backscattered from biological tissue at different depths, theimage displayed on the monitor corresponds to an image of biologicaltissue under study. The biological tissue basal membrane, whichseparates the epithelium from underlying stroma, is identified in theacquired image. Diagnostics is made on basis of the state of the basalmembrane.

Diagnostics of biological tissue with the aid of the method of theinvention is illustrated with several clinical cases, whereas theexamination of patients took place in hospitals of Nizhny Novgorod(Russia).

Namely, an examination of women, which had no pathology in the uterinecervix, with the aid of the developed method allowed obtaining images ofhealthy epithelium of the uterine cervix (FIGS. 7A and 7B). It can beseen from these images that biological tissue covered with healthyepithelium 45 has a smooth basal membrane 46, which separates stratifiedsquamous epithelium 45 from underlying connective tissue 47.

It can be seen from images shown in FIG. 7C and 7D that pathologicalregions of biological tissue are characterized by a change in the shapeof the basal membrane 46, or violation of its integrity, or its absolutedestruction.

FIG. 7C shows an image of a pathological region of the uterine cervix,obtained with the aid of the developed method, of a female patient I.,31 years old, in which there can be seen appendages of the basalmembrane 46 in an arc form, i.e. an alteration of the shape of the basalmembrane 46 not affecting its integrity. The clinical diagnostics offemale patient I. was precancer of uterine cervix. Standard colposcopytechnique revealed a phenomenon known as so-called mosaic. Informationobtained with target biopsy and subsequent morphological study of biopsymaterial provided grounds for diagnosing cervical intraepithelialneoplasia of the II degree.

FIG. 7D shows an image of a pathological region of the uterine cervix,obtained with the aid of the developed method, of a female patient G.,25 years old, in which there can be distinctly indicated structuralchanges in stratified squamous epithelium 45 and different extents ofchanges in the basal membrane 46. Female patient G. was admitted to theclinic for a suspicion for uterine cervix cancer T1 a. During thefurther course of treatment the patient underwent conization (i.e.,conical removal of pathological region) in the uterine cervix. Based onthe results of morphological study of the removed material thediagnostics was made as follows: cervical intraepithelial neoplasia ofthe III degree with transition into cancer in situ and microcarcinoma.It is well known from morphological research that exactly this stage inthe development of malignant process originating in the basal andparabasal layers of cells is accompanied by alterations in shape and anoccurrence of microruptures of the basal membrane.

FIG. 7E presents a tomographic image of a tumor region where the basalmembrane is not seen. This image was obtained with an examination of afemale patient M., 66 years old that was admitted to the clinic foruterine cervix cancer T1 b. This diagnostics was made clinically andconfirmed morphologically based on the results of biopsy.

Thus, the above examples demonstrate a possibility for using thedeveloped method for studying biological tissue in vivo in diagnosticsof different stages of uterine cervix cancer.

FIG. 8A and FIG. B illustrate opportunities to obtain images of otherhuman biological tissues with the aid of the apparatus and lateralscanner of the present invention. In particular, FIG. 8A demonstrates atomographic image of a front abdominal wall obtained during alaporoscopic examination of a female patient E., 22 years old. On thistomographic image one can see the serous membrane 37 with a layer ofconnective tissue, characterized by high reflectivity of opticalradiation, the subserous layer 38 including loose connective tissue andblood vessels 39, characterized by low reflectivity of opticalradiation, and underlying muscle layers 40.

FIG. 8 b shows a tomographic image of a tooth of a patient K., 56 yearsold, on which one can distinctly see the enamel 41, dentine 42, theboundary enamel-dentine 43 and a compomer filling 44.

INDUSTRIAL APPLICABILITY

The invention can be applied for medical diagnostics of individualorgans and systems of human body in vivo, for example, of hard-to-accesscavities and internal organs, as well as for industrial diagnostics, forinstance, for control of technological processes. It should be notedthat the invention can be implemented with using standard means.

1. The method wherein the determining step comprises a method ofdetection selected from the group consisting of absorbancespectrophotometry, fluorescence spectroscopy, fluorescence microscopy,epifluorescence microscopy, light microscopy, phosphorimaging andnephelemetry.
 2. The method of claim 1, wherein the determining stepfurther comprises a staining of the mutant fungal cells to aid indetection.
 3. The method of claim 2, wherein the staining is performedwith a dye selected from the group consisting of a fluorogenic compound,a naturally fluorescent compound, a calorimetric compound, achemiluminescent compound, a radioactive compound and combinationsthereof.
 4. The method wherein a plurality of test compounds are assayedin parallel.
 5. The method of claim 2, further comprising the steps of:(e) providing a population of host cells selected from the groupconsisting of mammalian cells and plant cells; (f) incubating the cellsunder growth conditions; (g) contacting the cells with the potentialantifungal agent identified in step (d); (h) determining whether thepotential antifungal agent inhibits growth of the cells indicating thatthe potential antifungal agent is toxic to host cells.
 6. The method ofclaim 5, wherein the potential antifungal agent does not inhibit growththe host cells.
 7. The method of claim 6, wherein the potentialantifungal agent is an antifungal therapeutic.
 8. The method of claim 6,wherein the host cells are human cells.
 9. The method of claim 5,wherein the mutant fungal cells are of a genus selected from the groupconsisting of Aspergillus, Saccharomyces, Cryptococcus, Histoplasma, andCandida.
 10. The method of claim 2, wherein the genetic mutationshyper-stabilize microtubules.